Sealant is often used in the aircraft industry to seal gaps and fill holes in or between parts. Sealant is typically loaded into disposable, cylindrical, plastic tubes, each having an open end on which a nozzle may be placed. A moveable plunger at the opposite end of the tube causes sealant to extrude out of the nozzle when pressed against the sealant.
Several types of sealant dispensing mechanisms have been developed for actuating the plungers of sealant tubes. Manually-operated sealant guns include a manually operated trigger or other mechanism for pushing a plunger to urge sealant from a sealant tube. Such manually-operated sealant guns are slow to operate and require large amounts of manual force to be effectively used in large scale manufacturing operations such as aircraft manufacturing plants.
Electric-powered sealant guns use motors or pistons to dispense sealant more quickly and with less manual effort than manually-operated sealant guns, but they are relatively large, heavy, and cumbersome and are therefore not ideal for use in confined or hard-to-reach spaces.
Pneumatic sealant guns employ pressurized air to move the plungers in sealant tubes and are typically lighter, more compact, and therefore easier to operate than electric-powered sealant guns or electro-mechanical sealant guns. However, pneumatic sealant guns can introduce unwanted air into sealant, resulting in air bubbles and related deformities in the extruded sealant. Extruded sealant that contains air bubbles often must be removed and re-applied, especially when used on aircrafts and other high value items. Removing extruded sealant from an aircraft or other component is costly and time-consuming. To avoid this, many workers only use a portion of the sealant in a tube and then dispose of the rest, because air bubbles more commonly form in the last portion of the sealant dispensed from a tube. This is wasteful, costly, and only partially effective, because air bubbles can infiltrate further into a sealant tube.